The present invention relates to degaussing, more particularly to closed loop degaussing (CLDG) of naval vessels.
The objective of a ship degaussing system is to maintain minimal magnetic signatures of a ship in order to maintain minimal susceptibility of the ship to magnetic mines. To this end, a ship degaussing system will seek to compensate for the ship's own magnetic signature as well as for the induced magnetism associated with the ship's navigation through the earth's magnetic field. Typically, the conventional (non-CLDG) system includes compensation coils, a single total-field magnetometer mounted on the mast, an automatic controller, power amplifier units and power supply units that control DC currents in the compensation coils.
The U.S. Navy has developed a closed loop degaussing (abbreviated “CLDG” for “Closed Loop De-Gaussing”) system that actively compensates for the induced and permanent magnetic signals of a ship. Essentially, CLDG is an onboard electromechanical system that measures onboard local magnetic fields and, using the onboard measurements, estimates the offboard magnetic fields. CLDG basically involves coil design, modern electronics and computer technology (including algorithmic control). The apparatus needed to perform CLDG includes onboard magnetometers, degaussing coils, analog-to-digital conversion/control equipment and a processing computer to execute the CLDG algorithm. Degaussing coils are already installed as standard items aboard many modern U.S. Navy ships.
Not unlike a conventional degaussing (non-CLDG) system, a closed loop degaussing (CLDG) system employs degaussing coils for conducting electrical current. However, in contrast to conventional (non-CLDG) degaussing, closed loop degaussing involves a computerized feedback control system that, in real time on a continual basis, compensates for the changes in the ship's magnetization on the basis of onboard magnetic measurements. CLDG implements an array of magnetic field sensors situated throughout the ship. During navigation, these onboard sensors constantly monitor the magnetic environment of the ship so as to detect variations in the ship's magnetic signature.
In principle, as compared with conventional (non-CLDG) degaussing systems currently installed on many Navy ships, CLDG can afford more accurate control of degaussing currents for purposes of minimizing the ship's magnetic signature, and can permit longer ship deployment periods between calibrations at degaussing facilities such as degaussing ranges. The CLDG algorithm currently installed aboard two U.S. Navy ships has a theoretical inaccuracy of about ten percent. It is desirable to have a CLDG system that affords greater accuracy than does the current CLDG system.
The following United States patents are incorporated herein by reference: Schneider, “Closed-Loop Multi-Sensor Control System and Method,” U.S. Pat. No. 5,189,590, issued 23 Feb. 1993; Holmes et al., “Zero Field Degaussing System and Method,” U.S. Pat. No. 5,463,523, issued 31 Oct. 1995; Holmes et al., “Advanced Degaussing Coil System,” U.S. Pat. No. 5,483,410, issued 9 Jan. 1996; Scarzello et al., “Integrating Fluxgate Magnetometer,” U.S. Pat. No. 6,278,272 B1, issued 21 Aug. 2001; Holmes et al., “Standing Wave Magnetometer,” U.S. Pat. No. 6,344,743 B1, issued 5 Feb. 2002. Scarzello et al., “Spatially Integrating Fluxgate Magnetometer Having a Flexible Magnetic Core,” U.S. Pat. No. 6,416,665 B1, issued 9 Jul. 2002; Scarzello et al., “Fluxgate Magnetic Field Sensor Incorporating Ferromagnetic Test Material into Its Magnetic Circuitry,” U.S. Pat. No. 6,456,069 B1, issued 24 Sep. 2002.